Microproteins Tracking: When Size Does Really Matter

Microproteins are a large, relatively underexplored group of proteins with unclear classification criteria. Their primary distinguishing feature is their small size, typically ranging from 7–20 kDa range. This fact imposes certain limitations on available methods of functional research in the field of microproteins: (i) during proteome experiments, they are difficult to detect in total protein mass, (ii) their isolation is complicated; (iii) they are hard to track with conventional bioengineering tools such as fluorescent proteins, as most of the labels are larger than the microproteins themselves. Several sophisticated approaches were developed to search and validate small proteins in translatome and proteome studies, of which the best known are deep sequencing and mass spectrometry-based methods. However, there is still a lack of efficient tools to investigate their actual biological form and function. Here, we review the existing methods for the detection and study of proteins, whose sizes are significantly smaller than the average, and propose possible tools that have not yet been applied, but hold a high potential in this field.